1. Field of the Invention
The present invention relates to a driving device of a vibration type actuator, and more particularly, to a driving device of a vibration type actuator for exciting and vibrating an electro-mechanical energy conversion element by applying a periodic signal to the element and obtaining a driving force.
2. Related Background Art
There is a vibration type actuator constructed by plural piezoelectric elements having polarities inverted to each other and a vibration member adhered to these piezoelectric elements as one form of the vibration type actuator. Alternating signals of two phases having a phase difference of 90 degrees to each other are applied to each of the piezoelectric elements. Thus, a traveling wave is generated on the vibration member. When a moving member is brought into press contact with the vibration member, the moving member can obtain a driving force by a frictional force.
In comparison with an actuator using an electromagnetic force, the vibration type actuator has such a characteristic that driving torque at low speed is larger and responsiveness is better and it is sufficiently quiet for a user to be unaware of a driving sound since vibration in a frequency range equal to or greater than an audible range is utilized. Since the vibration type actuator has such features, the vibration type actuator may be used, e.g., in a driving section of an image printer.
The vibration type actuator generally requires a large alternating voltage. One method for obtaining the large alternating voltage is amplifying a driving signal using a linear amplifier; another method is raising a voltage using a transformer; yet another method is utilizing resonance with a capacity component of the vibration type actuator by combining an inductance element and a switching element with each other. The voltage may be raised using one of these methods, or by combining plural methods with each other.
The method of raising the voltage using a transformer and the method of switching and raising the voltage by combining an inductance element and a switching element with each other are preferably used among the above methods since these two methods are excellent in view of efficiency, cost, space, and the like.
However, higher harmonic waves of the driving signal are always included in a driving signal in which the voltage is raised using switching. These higher harmonic waves do not contribute to driving. Instead, it is feared that these higher harmonic waves become useless energy loss, cause heating of the actuator, cause undesirable vibration, and become a noise source. In the switching system, a waveform is generally smoothed by matching of the inductance element and the capacity component of the vibration type actuator, but a larger higher harmonic wave component causes useless heating of the inductance element.
A method for raising the voltage by generating a driving pulse signal based on a pulse signal having a frequency four times the driving frequency is shown in Japanese Patent Application Laid-Open Nos. 63-1379 and 63-262070. In this method, the duty of the pulse signal is limited to 25% or 50% and a driving operation having preferable energy conversion efficiency can not be performed, since there are many higher harmonic wave components.
A method for modulating a pulse width is shown in Japanese Patent Application Laid-Open No. 4-140075. In this method, efficiency is not necessarily good and a driving operation that reduces generation of noises can not necessarily be performed.
The present invention has been made in view of the foregoing problems, and therefore has an object thereof to provide a driving device having a vibration type actuator for improving electro-mechanical energy conversion efficiency and reducing generation of noise.
One aspect of the present invention resides in a driving device of a vibration type actuator for obtaining a driving force by exciting an electro-mechanical energy conversion element by applying a periodic signal to the electro-mechanical energy conversion element, comprising: a D.C. power source; plural switching elements connected to the D.C. power source; an inductance element connected to the plural switching elements for raising the voltage; and a drive control circuit for generating a switching pulse for operating the plural switching elements, wherein each of the plural switching elements is operated by the switching pulse generated by the drive control circuit, and the drive control circuit selects a width of the generated switching pulse so as to set the amplitude of a base wave frequency component among frequency components of a voltage applied to the inductance element to be larger than a total amplitude of higher harmonic wave frequency components.
Another aspect of the present invention also resides in a driving device of a vibration type actuator for obtaining a driving force by exciting an electro-mechanical energy conversion element by applying a periodic signal to the electro-mechanical energy conversion element, comprising: a D.C. power source; plural switching elements connected to the D.C. power source; an inductance element connected to the plural switching elements for raising the voltage; and a drive control circuit for generating a switching pulse for operating the plural switching elements, wherein each of the plural switching elements is operated by the switching pulse generated by the drive control circuit, and the drive control circuit selects a width of the generated switching pulse so as to set at approximately a maximum value an amplitude ratio of a base frequency component to a total amplitude of higher harmonic wave frequency components of a voltage applied to the inductance element.
Another aspect of the present invention also resides in a driving device of a vibration type actuator for obtaining a driving force by exciting an electro-mechanical energy conversion element by applying a periodic signal to the electro-mechanical energy conversion element, comprising: a D.C. power source; plural switching elements connected to the D.C. power source; an inductance element connected to the plural switching elements for raising the voltage; and a drive control circuit for generating a switching pulse for operating the plural switching elements, wherein the drive control circuit gradually increases a width of the generated switching pulse from zero at a rising time and operates the plural switching elements by the switching pulse so that the drive control circuit sweeps the pulse width until an amplitude ratio of a base wave frequency component to a total amplitude of higher harmonic wave frequency components of a voltage applied to the inductance element is approximately maximum, and the drive control circuit fixes the pulse width in this state.
Another aspect of the present invention resides in a driving device of a vibration type actuator for obtaining a driving force by exciting an electro-mechanical energy conversion element by applying a periodic signal to the electro-mechanical energy conversion element, comprising: a D.C. power source; plural switching elements connected to the D.C. power source; and a drive control circuit for generating a switching pulse for operating the plural switching elements, wherein each of the plural switching elements is operated by the switching pulse generated by the drive control circuit, and the drive control circuit selects a width of the generated switching pulse so as to set the amplitude of a base wave frequency component among frequency components of a voltage applied to the electro-mechanical energy conversion element to be larger than a total amplitude of higher harmonic wave frequency components.
Another aspect of the present invention resides in a driving device of a vibration type actuator for obtaining a driving force by exciting an electro-mechanical energy conversion element by applying a periodic signal to the electro-mechanical energy conversion element, comprising: a D.C. power source; plural switching elements connected to the D.C. power source; and a drive control circuit for generating a switching pulse for operating the plural switching elements, wherein each of the plural switching elements is operated by the switching pulse generated by the drive control circuit, and the drive control circuit selects a width of the generated switching pulse so as to set an amplitude ratio of a base frequency component to a total amplitude of higher harmonic wave frequency components of a voltage applied to the electro-mechanical energy conversion element to be approximately maximum.
Another aspect of the present invention resides in a driving device of a vibration type actuator for obtaining a driving force by exciting an electro-mechanical energy conversion element by applying a periodic signal to the electro-mechanical energy conversion element, comprising: a D.C. power source; plural switching elements connected to the D.C. power source; and a drive control circuit for generating a switching pulse for operating the plural switching elements, wherein the drive control circuit gradually increases a width of the generated switching pulse from zero at a rising time and operates the plural switching elements by the switching pulse so that the drive control circuit sweeps the pulse width until an amplitude ratio of a base wave frequency component to a total amplitude of higher harmonic wave frequency components of a voltage applied to the electro-mechanical energy conversion element is approximately maximum, and the drive control circuit fixes the pulse width in this state.
Another aspect of the present invention resides in a driving device of a vibration type actuator for obtaining a driving force by applying a periodic signal to an electro-mechanical energy conversion element portion arranged in a vibration member, comprising: a switching element switched in response to a pulse signal; an inductance element through which an electric current intermittently flows by switching the switching element; and setting means for applying a voltage generated by intermittently flowing the electric current through the inductance element to the electro-mechanical energy conversion element portion, and setting a duty of the pulse signal to a duty in which a base frequency component among frequency components of a voltage applied to the inductance element is larger than a higher harmonic wave component.